The invention relates to a gear-shift control of bicycles and similar vehicles. This invention relates to the "rear" gear-shift control as well as to the "front" gear-shift control and it applies, more specifically, to gear shifts of the "derailleur" type, in which modification of the gear ratio is obtained by passage of the chain from one sprocket to another, in the case of a rear derailleur associated with a free wheel, or by passage of the chain from one toothed plate to another, in the case of a front derailleur associated with the crankset.
The rear or front derailleurs are controlled manually remotely, in the conventional way, by a cable ending at a pivoting shifter placed either on a tube of the bicycle frame or on an end of the bicycle handlebars. As a function of the angular position of the shifter, the chain passes on a certain sprocket, in the case of a rear derailleur, or on a certain plate, in the case of a front derailleur; thus, depending on the number of existing sprockets or plates, the shifter has several corresponding angular positions.
The result is that the handling of the shifter is difficult to understand and to learn, notably for beginners, the angular positions of the shifter being difficult to identify precisely in the usual absence of indexing means, and the direction and angles of rotation of the shifter that are necessary to obtain passage from one sprocket or from one plate to another being poorly understood. In the case of the rear derailleur, the correct angular positions of the shifter can be poorly perceived the more sprockets there are, these positions then being very close to each other. In the case of the front derailleur, an additional difficulty results from the fact that the direction of maneuvering the shifter is opposite to that of the rear derailleur: the cyclist must pull the shifter of the front derailleur toward himself, while pushing away the shifter of the rear derailleur to obtain, in the two cases, a higher gear.
Incorrect handling of the shifters that control the derailleurs is not without consequences. In particular, wrong positioning of the chain is the source of friction, disagreeable noises and, worse, jumps by the chain at the moment when the cyclist produces significant effort, which can cause a swerving of the cyclist, even a fall.